Biomedical subjects

M Geysen

Publications and source records attributed to M Geysen.

8 recordsLinked to original sources

PubMed1996

Unique role of thyroxine in T cell recognition of a pathogenic peptide in experimental autoimmune thyroiditis.

We have previously demonstrated the importance of iodination and the requirement of the thyroxine residues in thyroglobulin (Tg) for the stimulation of two clonotypically distinct murine T cell hybridomas reactive against human and mouse Tg. We are now able to show that these T cell hybridomas only recognize an 11-residue peptide containing a thyroxine structure that has iodine at two positions on each ring. This iodination state is critical for recognition by these hybridomas as a peptide containing de-iodinated thyroxine is nonstimulatory. Furthermore we have demonstrated that a peptide lacking the thyroxine residue or containing de-iodinated thyroxine cannot block the recognition of the thyroxine-containing peptide. We suggest that in our system the thyroxine residue is involved in binding to major histocompatibility complex (MHC) class II molecules. We have also been able to show that the thyroxine residue is available for contact by the T cell receptor (TCR) as recognition of the peptide/H-2A(k) complex is blockable by an antibody directed against thyroxine. Using substituted peptides, we have been able partially to define the residues within the peptide that are critical for recognition of the 11-residue peptide by our hybridomas. From our data, we suggest that the thyroxine residue may bind the MHC and TCR, while the residues identified in the peptide backbone as important for the stimulation of the hybridomas may bind only the TCR.

Amino Acid Sequence↗

PubMed1994

Immunodominant epitopes of glutamic acid decarboxylase 65 and 67 in insulin-dependent diabetes mellitus.

To find the dominant epitopes of a major autoantigen in insulin-dependent diabetes mellitus (IDDM), glutamic acid decarboxylase (GAD), we studied the reactivity of peripheral blood T lymphocytes with peptides covering both major isoforms. A significant response to GAD 65 or GAD 67 peptides was detected in 13 of 15 IDDM patients and in 9 of 10 normal controls. Controls most frequently recognised the central region of GAD 65 (residues 161-243). IDDM patients preferentially recognised residues 473-555 (p < 0.03). T-cell responses to GAD 67 peptides were similar in IDDM patients and controls. T lymphocytes from IDDM patients recognise a distinct dominant epitope of GAD, which may be an important target for the disease process.

Adolescent↗

PubMed1994

Comprehensive T-cell epitope mapping of HIV-1 env antigens reveals many areas recognized by HIV-1-seropositive and by low-risk HIV-1-seronegative individuals.

Peripheral blood mononuclear cells from 12 asymptomatic human immunodeficiency virus (HIV)-1-seropositive and nine HIV-1-seronegative donors were screened for proliferative T-lymphocyte responses to peptides derived from a consensus sequence of the HIV-1 env gene products from 25 HIV-1 isolates. Two hundred seventy-eight overlapping 17mer peptides, incremented by three residues each, were pooled into groups, each containing eight sequential peptides, for use in proliferation tests. Thirty-eight additional peptides containing variant amino acid residues also were tested. Proliferation data were analyzed using an algorithm that reduced subjective bias and estimated the responding cell frequencies. Peripheral blood mononuclear cells from a majority of donors, regardless of HIV-1 status, recognized peptides within two pools derived from the gp120 sequence and peptides from one pool in gp41. Pool 25 peptides from gp41 (centered around residue 600 of the gp160 consensus sequence) were recognized most frequently. The observed inability to differentiate between responses of HIV-1-seropositive and HIV-1-seronegative individuals implies either a lack of HIV-1 disease-related immunodominant env epitopes or functional abrogation of HIV-1 env-specific T-helper lymphocyte responses soon after infection. The observed proliferation of T lymphocytes from noninfected, low-risk individuals questions the origin of the responses to HIV-1 env-derived peptides and suggest that preexisting, cross-reactive immunity could influence responses to HIV-1.

Adult↗

PubMed1993

T cell epitopes of the major fraction of rye grass Lolium perenne (Lol p I) defined using overlapping peptides in vitro and in vivo. I. Isoallergen clone1A.

One hundred and fifteen overlapping synthetic peptides spanning the entire sequence of the iso-allergen clone1A of Lol p I from rye grass Lolium perenne were synthesized by the multi-pin technique. The peptides were overlapping 12mers, offset by two residues and overlapping by 10 residues. Sets of six adjacent overlapping peptides (except pool-1, 15, 20) were pooled and were used in vitro and in vivo to map the T cell epitopes on Lol p I. Six atopics who were skin test and RAST positive to rye grass showed T cell responses to L. perenne extract (LPE) and its major fraction (Lol p I). Five out of six showed T cell responses in vitro to peptide pool-17, while five non-atopics did not respond to any of the peptide pools. By testing the individual peptides of pool-17, we have located the T cell epitope on Lol p I. Interestingly, when we tested pool-17 and its single peptides in vivo by intradermal skin testing we found in one patient a typical DTH after 24-48 h to pool-17 and its peptides (peptides 3 and 4) which exactly matched the in vitro responses. By defining the T cell epitopes in this way a greater understanding of the allergic response to pollen will be obtained, and a more effective and less dangerous vaccine may be possible for treating patients with hay fever.

Adult↗

PubMed1992

A thyroxine-containing peptide can induce murine experimental autoimmune thyroiditis.

A synthetic peptide based on a sequence containing thyroxine at position 2553 in thyroglobulin (Tg), and already shown to be recognized by two clonotypically distinct murine Tg autoreactive T cell hybridomas, can trigger primed lymph node cells to transfer thyroiditis to naive recipients. Donor lymph node cells could be prepared from mice immunized either with intact mouse Tg or with this peptide itself. After a second exposure to the priming antigen in vitro, both these populations induced 100% thyroiditis in recipient animals. The importance of the T4 residue in the development of disease was demonstrated by the failure of Tg tryptic peptides depleted of T4 to stimulate pathogenic effectors in vitro, even when the lymph node cells had been taken from mice primed with whole Tg. We conclude that this T4-containing 12mer sequence is a major thyroiditogenic epitope in CBA/J mice although we cannot exclude the possibility that there are other pathogenic epitopes present in the whole Tg molecule.

Animals↗

PubMed1991

Identification of a thyroxine-containing self-epitope of thyroglobulin which triggers thyroid autoreactive T cells.

Although thyroglobulin (Tg), the thyroid prohormone, is well known as a T cell dependent autoantigen in human and experimental autoimmune thyroid disease, very little is known about the molecular basis of Tg recognition by T cells. In this paper, we have characterized the epitopes recognized by two clonotypically distinct, murine Tg autoreactive T cell hybridomas, CH9 and ADA2. In vitro iodination of a Tg preparation which was deficient in in vivo organified iodine was first used to confirm our previous observation that these T cells recognize iodination-related epitopes in the Tg molecule. Affinity chromatography of tryptic peptides derived from normally iodinated human Tg revealed that these epitopes were exclusively located in thyroxine (T4) containing peptides. Through the use of synthetic T4-containing peptides, representing the four major hormonogenic sites in Tg, we demonstrated that both CH9 and ADA2 recognize an epitope containing the T4 at position 2553 in human Tg. Sets of overlapping 5mer to 12mer peptides around this T4 showed that the most potent peptide was a 9mer beginning at Asp 2551. The T4 was shown to be a critical residue, since its replacement with any of the 20 naturally occurring amino acids produced only nonstimulatory peptides. Since the T cell hybridomas could also be stimulated by major histocompatibility complex class II positive (interferon-gamma-treated) thyroid epithelial cells in vitro, and their parent T cell lines can induce thyroiditis on adoptive transfer, the T4-containing Tg sequence described here is implicated as a pathogenic epitope in murine thyroid autoimmunity.

Amino Acid Sequence↗

PubMed1989

Immune response to a synthetic peptide corresponding to an epitope of a parasitophorous vacuole membrane antigen from Plasmodium falciparum.

The parasitophorous vacuole membrane antigen QF 116 from Plasmodium falciparum contains a defined epitope, DNNLVSGP, proximal to the carboxyl-terminus which binds to the inhibitory monoclonal antibody 8E7/55. A synthetic peptide containing this epitope was constructed and coupled to diphtheria toxoid as carrier. Mice and rabbits were inoculated with this conjugate using CFA, SAF-1, or aluminum phosphate as adjuvants. The peptide conjugate was highly immunogenic in both animal species, giving rise to polyclonal antibodies with a similar epitope specificity as the original mAb. Antibody titers were dependent on the route of immunization. Rabbit antibodies produced in sufficient quantity for biologic assays inhibited parasite growth in vitro. This synthetic peptide thus shows promise as an immunogen for use in synthetic vaccine design.

Amino Acid Sequence↗

PubMed1989

A protective monoclonal antibody recognizes a linear epitope in the precursor to the major merozoite antigens of Plasmodium chabaudi adami.

The monoclonal antibody 5C10/66 was shown to afford strong protection in mice against fulminating Plasmodium chabaudi adami infection. This was remarkable, as immunity to this organism is regarded to be mainly T-cell mediated. This antibody identified a 250-kDa molecule in schizonts and an 83-kDa fragment in merozoites. A cDNA clone selected by 5C10/66 was the homologue of the Plasmodium falciparum precursor to the major merozoite surface antigen (PMMSA). Comparison with the P. falciparum sequence showed that the P. chabaudi adami clone encoded the middle portion of the gene and that it can also be divided into variable and conserved blocks. Screening of a set of all possible octamer peptides predicted by the cDNA clone revealed that the core epitope of 5C10/66 was Glu-Thr-Thr-Glu-Thr. This region resides in a variable block of PMMSA.

Amino Acid Sequence↗